Currently, the API is only available to get list of canvas apps from an environment. Even in PowerShell it uses underlying web API's to get all the details.
For "Get-AdminPowerApp" the user which you used for authentication, is he an environment admin? As per docs, it mentioned as "Returns all apps from all environments where the calling user is an Environment Admin". if he is, then the API is available only for canvas app.
If it answers you question, Kindly give kudo and mark it as solution.